The present invention relates to an electrical control system for a vehicle and particularly one for use in connection with a display of the vehicle's heading.
In recent years, digital electronics technology has been employed in the automotive industry to provide, for example, the display of speed and engine operating parameters to the vehicle user.
In a compass for use in a vehicle, it is necessary to compensate the compass to correct for stray magnetic fields and ferromagnetic material in the vicinity of the sensor. For accuracy, a second and different correction for variation in the earth's magnetic field as a function of the geographic location of the vehicle is desirable. Thus, for example, in the United States, the magnetic variation between true north and magnetic north from the east to west coast is approximately 40.degree.. Thus, a compass system installed in a vehicle which may travel in various parts of the country during use should include means for correcting for the earth's magnetic field variation as well as means for compensating for the particular installation of the compass in an individual vehicle.
Typically, vehicle mounted compasses have been mechanical types with rotating compass cards mounted in a viscous damping media. An electrical compass has been described in a 1980 SAE paper entitled Magnetic Field Sensor and Its Application to Automobiles by Hisatsugu Itoh, SAE/SP-80/458. This compass employs a flux-gate sensor and solid state circuits and compensation correction only is provided by manually adjustable potentiometers in a circuit coupled to the flux-gate sensor. U.S. Pat. No. 4,030,204 discloses a vehicle automotive compass in which Hall effect sensors are employed and in which compensation is provided by the utilization of conventional adjustably mounted magnets as frequently employed in conventional vehicle compasses employing movable compass cards.